M4 carbine

The M4 carbine (officially Carbine, Caliber 5.56 mm, M4) is an assault rifle developed in the United States during the 1980s. It is a shortened version of the M16A2 assault rifle. The M4 is extensively used by the U.S. military, which decided to largely replace the M16 rifle in U.S. Army (starting 2010) and U.S. Marine Corps (starting 2016) combat units as the primary infantryservice rifle. The M4 has been adopted by over 60 countries, and has been described as "one of the defining firearms of the 21st century".

Since its adoption in 1994, the M4 has undergone over 90 modifications to improve the weapon's adaptability, ergonomics and modularity, including the M4A1 variant, which possesses a thicker barrel and a replacement of the burst-fire control group with a fully automatic one; the SOPMOD, an accessory kit containing optical attachments; and the underbarrel weapons such as M203 and M320grenade launchers to the Masterkey and M26-MASSshotguns.

In April 2022, the U.S. Army selected the M7 rifle, a variant of the SIG MCX Spear, as the winner of the Next Generation Squad Weapon Program to replace the M16/M4.